You need a HID device that declares itself as a scanner reader (one of the sub classes within HID). I'm not sure you will find a generic off-the-shelf converter that happens to be programmed as a QR...

It looks like FT260 may but this looks even simpler and promising what do you guys think http://www.holtek.com.tw/documents/10179/11842/HT42B564-xv110.pdf this sounds like it should be fairly easy to...